1. Field of Invention
The present invention relates generally to optical imaging systems that monitor oxygen levels in tissue. More specifically, the present invention relates to monitoring oxygen levels to determine the viability of flaps before and after a flap transplant.
2. Description of the Related Art
Flap surgery is a type of plastic or reconstructive procedure that enables tissue from one area of a body to effectively be moved to another area of the body. A flap is a section of living tissue with a blood supply that may be transported from a “donor” area of a body to a new area of the body, i.e., an area onto which the flap is to be transplanted. A flap may be transplanted to an area of the body that has lost, for example, skin, fat, or muscle. Flap surgery generally restores some muscle movement or skeletal support to an area in which muscle movement or skin coverage may have been missing.
There are many different kinds of flaps that are used in flap surgery. A local flap is typically a piece of skin with underlying tissue that is located next to a wound. The local flap is repositioned over the wound while remaining attached at one end such that the local flap may be nourished by its original blood supply. A regional flap is generally a section of tissue that is attached by a specific blood vessel or specific blood vessels. When lifted, the regional flap uses a relatively narrow attachment to the donor, or original, site to receive a blood supply from the specific blood vessel or vessels, e.g., a tethered artery and vein. A musculocutaneous flap, i.e., a muscle and skin flap, is typically used when an area to be covered by the flap is relatively large and requires a significant blood supply. A musculocutaneous flap is often used in breast reconstruction surgery, and remains tethered to its original blood supply. A microvascular free flap is a flap of tissue and skin that is detached, along with blood vessels, from an original site of a body and reattached to a new site in the body. As a microvascular free flap is completely detached from an original site, the attachment of such a flap to a new site requires reattaching severed blood vessels at the new site.
Blood flow through transplanted flaps may change drastically in the period of time substantially immediately after a transplant is completed. A transplanted flap may sometimes die, i.e., transplanted tissue may die, when the blood flow through the transplanted flap is compromised. For example, a blood clot in the transplanted flap or a pinched vein in the transplanted flap may cause the transplanted flap to die. Currently, to monitor a transplanted flap to determine whether blood flow through a transplanted flap is adequate to sustain the transplanted flap, laser Doppler flap monitoring may be used. Laser Doppler flap monitoring, or laser Doppler flowmetry, allows Doppler measurements to be made near blood vessels of the transplanted flap. Interpretation of the Doppler measurements may enable potential flap failures to be detected before clinical signs of failure, e.g., discoloration of the transplanted flaps, manifest themselves.
Though laser Doppler flap monitoring may be effective for enabling potential flap failures to be detected in some instances, laser Doppler systems are generally able to make measurements on relatively large vessels, and are unable to measure regional perfusion in the micro-vasculature within a skin flap. Even though flow may be detected in larger vessels when laser Doppler flap monitoring is employed, distal flap tissue may be underperfused and, as a result, may die.
As an alternative to laser Doppler flap monitoring, some surgeons may nick a transplanted flap in various places to assess the blood flow therethrough. Nicking a transplanted flap is invasive and does not always allow for an accurate determination of the viability of a transplanted flap, as assessing the blood flow in such a manner is highly subjective. Further, it may be very difficult to determine where in a transplanted flap to make a nick, e.g., a surgeon may inadvertently fail to make a nick near a blood vessel that is pinched.
Therefore, what is needed is a method and an apparatus which allows the viability of a transplanted flap to be accurately determined. That is, what is desired is a system which is non-invasive and relatively non-subjective, and allows the blood flow through a flap to be accurately assessed.